The invention relates to a flame-retarding composition and a process for the preparation thereof.
A flame-retarding composition and a process for the preparation thereof are for example described in the Japanese patent publication JP 59-45352, in which the melamine condensation products melem and melon are prepared and used as flame retardants in polyamide compositions. In this publication melem is prepared by heating melamine at a temperature of 400-500xc2x0 C. for several hours. Melon is prepared by heating melamine at 500-550xc2x0 C. until no more ammonia is released. JP 59-45352 mentions that the decomposition temperature of melem lies above 500xc2x0 C. and that of melon above 600xc2x0 C. This means that melem and melon have a particularly good thermal stability. According to JP 59-45352, the nitrogen contents of both compounds lie above 60%, as a result of which the substances are non-combustible. JP 59-45352 also mentions that other known flame retardants can also be used in combination with melem or melon, for example melamine, cyanuric acid, melamine cyanurate or melam. JP 59-45352 does not mention the composition of the product obtained.
Melamine and its condensation products all have a characteristic thermal degradation curve. This means that melamine and its condensation products decompose to form nitrogen-containing products at a certain temperature. These nitrogen-containing products that are released in the thermal degradation play an important part in the flame-retardant behaviour. To obtain good flame-retardant behaviour in polymers it may be favourable to combine flame-retarding components, such as melam, melem and the higher condensation products of melamine and/or melem, having different degradation characteristics, in a single composition. The advantage of this is that, irrespective of the temperature prevailing in a fire, there will almost always be a component present that degrades at the prevailing temperature and produces sufficient nitrogen-containing components having a flame-retarding effect. However, if the flame-retarding composition contains volatile components, such as urea and/or water, this will have a negative effect on the processing properties when the composition is used in polymers with a high melting temperature, for example in polyesters such as polyethylene terephthalate (PET) or polybutylene terephthalate (PBT) or in polyamides. Such a negative effect could be foaming during extrusion or the formation of deposits on the mould in injection-moulding. If the flame-retarding composition contains too high a concentration of higher condensation products of melamine and/or melem, the composition will be yellow, which is undesirable in the case of processing in (uncoloured) polymer compositions. The use of pure melamine condensation products such as pure melam or melem or melon as a flame retardant in polymers is unfavourable because it will usually be difficult, and hence expensive, to prepare pure compounds and because pure components have only one mode of degradation and will hence work optimally only in a limited temperature range.
The applicant has discovered that excellent processing properties and excellent flame-retarding properties and colour properties can be obtained in polymer compositions by using a flame-retarding composition containing:
10-90 wt. % melem,
0.01-30 wt. % melam,
0.01-15 wt. % melamine,
0.1-65 wt. % higher condensation products of melamine and/or melem, the concentration of volatile components being lower than 3 wt. % and the sum of the individual components amounting to 100 wt. %.
The concentration of volatile components is here defined as the decrease in weight that occurs in heating the flame-retarding composition from room temperature to 300xc2x0 C. in a TGA measurement (TGA=thermogravimetric analysis) at a heating rate of 200xc2x0 C. per minute.
The applicant has also found a process for preparing a flame-retarding composition comprising 10-90 wt. % melem, 0.01-30 wt. % melam, 0.01-15 wt. % melamine, 0.1-65 wt. % higher condensation products of melamine and/or melem, the concentration of volatile components being lower than 3 wt. % and the sum of the individual components amounting to 100 wt. %, by heating a starting product containing melamine, for example by passing it through a heating zone, for longer than 0.1 sec., preferably 1 sec. to 400 minutes, in particular 2 sec. to 300 minutes, at a temperature of 350-800xc2x0 C., preferably between 375 and 600xc2x0 C. and at a pressure between 1 KPa and 50 MPa, preferably between atmospheric pressure and 30 MPa, more in particular between atmospheric pressure and 15 Mpa.
Examples of heating zones are heating zones of the kind that are to be found in extruders, such as single- and twin-screw extruders; autoclaves; turbo mixers; plough blade mixers; tumble mixers; turbulence mixers; ribbon-blade mixers; mixtruders; continuous and discontinuous kneading machines; rotating drum ovens, etc.
A mixture of melamine, melem, melam and higher condensation products of melamine and/or melem can optionally be obtained by treating the product of the heating further, to obtain a flame-retarding composition comprising 10-90 wt. % melem, 0.01-30 wt. % melam, 0.01-10 wt. % melamine, 0.1-65 wt. % higher condensation products of melamine and/or melem, the concentration of volatile components being lower than 1 wt. % and the sum of the individual components amounting to 100 wt. %. This further treatment is preferably washing with water to dissolve and remove from the flame-retarding composition a portion of the melamine and/or other water-soluble components.
As the starting material for the present process, use can be made of virtually pure melamine, as for example obtained from a continuously operating gas-phase melamine plant where the melamine is purified by means of crystallisation. A method for the preparation of melamine via a gas-phase process is for example known from U.S. Pat. No. 3,210,352. This high degree of purity is however not necessary. Melamine contaminated with melam and/or melem and/or higher condensation products of melamine and/or melem can optionally be used as the starting material, for example the product that is formed during start-up of a melamine plant or melamine of the kind that is prepared in a gas-phase melamine plant before purification by means of crystallisation has taken place or melamine contaminated with melam and/or melem and/or higher condensation products of melamine and/or melem formed in some other way. It is also possible to use melamine obtained in a liquid-phase process as the starting material. A known process for the preparation of melamine via a liquid-phase process is described in U.S. Pat. No. 4,565,867, of which it is known that the degree of purity is less than that of the product of a gas-phase process; in particular, its melam content is higher. Contaminants like residual catalyst, ureidomelamine and/or guanidine carbonate may also be present without any objection. Oxygen-containing triazine compounds such as ammeline, ammelide and/or cyanuric acid may also be present up to 5 wt. % without any objection. Remains of the starting materials used for the preparation of melamine, such as urea and/or dicyanodiamide, may also be present; dicyanodiamide may be present up to 10 wt. % without any objection, while the melamine may contain up to 30 wt. % urea. The starting material for the present process may also contain contaminants containing mixtures of urea, oxygen-containing triazine compounds, dicyanodiamide, guanidine carbonate, ureidomelamine and residual catalyst.
In a preferred embodiment of the invention the flame-retarding composition is prepared by heating the melamine-containing starting product in an autoclave or in an extruder. Preferably at a pressure between atmospheric pressure and 20 Mpa, at a temperature of 350-625xc2x0 C. and with a residence time of between 0.1 sec. and 360 minutes. More in particular the heating of the melamine-containing starting product is carried out in an extruder with a residence time in the extruder of between 0.1 sec. and 60 minutes.
The invention also relates to flame-retarding polymer compositions comprising the following components:
a. 65-95 wt. % polymer-containing composition
b. 5-35 wt. % flame-retarding composition according to the invention
The flame-retarding composition according to the invention is particularly suitable for use in polymer compositions requiring heat-resistant flame retardants, for example in polyamides, polyimides, polyesters, styrene-containing polymers, epoxy resins, unsaturated polyester resins and polyurethanes.
Examples of polyamides are polyamides and copolyamides derived from diamines and dicarboxylic acids and/or from aminocarboxylic acids or the corresponding lactams, such as polyamide 4, polyamide 6, polyamides 6/6, 6/10, 6/9, 6/12, 4/6, 66/6, 6/66, polyamide 11, polyamide 12, partially aromatic (co)polyamides, for example polyamides based on an aromatic diamine and adipic acid; polyamides prepared from an alkylene diamine and iso- and/or terephthalic acid and copolyamides thereof, copolyether amides, copolyester amides, etc.
Examples of polyesters are polyesters derived from dicarboxylic acids and dialcohols and/or from hydroxycarboxylic acids or the corresponding lactones such as polyethylene terephthalate, polybutylene terephthalate, poly-1,4-dimethylolcyclohexane terephthalate, polyhydroxybenzoates, polycaprolactone and copolyesters thereof, copolyether esters, etc.
Examples of styrene-containing polymers are polystyrene, acrylonitrile-styrene copolymer, acrylonitrile-styrene-butadiene copolymers and mixtures hereof.
Preferably the flame-retarding composition is used in polyesters such as polyethylene terephthalate and/or polybutylene terephthalate, polybutylene terephthalate being particularly preferable, or in polyamides such as nylon-6, nylon 6,6 or nylon 4,6.
xe2x80x9cPolymer-containing compositionsxe2x80x9d are understood to be compositions which, in addition to polymer, may also contain reinforcing agents and/or fillers, compounds that have a synergetic effect with the flame-retarding composition, other flame-retarding components than those according to the invention, plus the usual additives.
If reinforcing agents and/or fillers are used in the polymer composition of the invention, their concentration may vary within a wide range, partly determined by the level of mechanical properties one wishes to achieve. In general, the concentration of reinforcing agents will be no more than 50 wt. % in the reinforced flame-retarding polymer composition. Preferably the reinforced flame-retarding polymer composition will contain 5-50 wt. % reinforcing agents, more preferably 15-45 wt. %. The reinforcing agents can be chosen from the group comprising inorganic reinforcing agents, such as mica, clay, talc or glass fibres, or aramide fibres and/or carbon fibres. Glass fibres are however preferable.
The flame-retarding effect of the flame-retarding composition according to the invention can be reinforced by the presence of a compound that has a synergetic effect with the flame-retarding composition, such as a carbon-forming compound, whether or not combined with a catalyst promoting the formation of carbon. In general the concentration of the flame-retarding composition can then be chosen to be lower.
In principle, all the known substances that reinforce the effect of flame-retarding compositions can be used as carbon-forming compounds. Examples are phenolic resins, epoxy resins, melamine resins, alkyd resins, allyl resins, unsaturated polyester resins, silicone resins, urethane resins, acrylate resins, polyphenylene ether, polycarbonate, starch, glucose and compounds containing at least two hydroxyl groups. Examples of compounds containing at least two hydroxyl groups are alcohols containing at least two hydroxyl groups, for example pentaerythritol, dipentaerythritol, tripentaerythritol and mixtures hereof. The concentration of the carbon-forming compound having a synergetic effect with the flame retardant in the overall polymer composition will generally lie between 0 and 30 wt. %, preferably between 1 and 20 wt. %.
As the catalyst promoting the formation of carbon use can for example be made of metal salts of tungstic acid; a complex acid oxide of tungsten with a metalloid; salts of tin oxide; ammonium sulphamate and/or the dimer hereof. Metal salts of tungstic acid are preferably alkali metal salts of tungstic acid, in particular sodium tungstate. A xe2x80x9ccomplex acid oxide of tungsten with a metalloidxe2x80x9d is understood to be complex acid oxides which are formed from a metalloid such as silicon or phosphorus and tungsten, such as silicotungstic acid or phosphorotungstic acid. The amount of catalyst promoting the formation of carbon that is used in the overall polymer composition is 0.1-5 wt %, preferably 0.1-2.5 wt %.
The flame-retarding effect of the flame-retarding composition according to the invention can be further reinforced by using one or more other flame-retarding components. In principle, all the known flame retardants can be used as the other flame-retarding components. Examples are antimony oxide, for example antimony trioxide, combined with halogen compounds; alkali earth metal oxides, for example zinc oxide, magnesium oxide; other metal oxides, for example alumina, silica, iron oxide and manganese oxide; metal hydroxides, for example magnesium hydroxide and aluminium hydroxide; metal borates, for example zinc borate, whether or not hydrated; and phosphorus-containing compounds. Examples of phosphorus-containing compounds are zinc phosphate, ammonium phosphate, ammonium pyrophosphate, ammonium polyphosphate, ethylene-diamine phosphate, piperazine phosphate, piperazine pyrophosphate, melamine phosphate, dimelamine phosphate, melamine pyrophosphate, melamine polyphosphate, melam phosphate, melam pyrophosphate, melam polyphosphate, melem phosphate, melem pyrophosphate, melem polyphosphate, guanidine phosphate, dicyanodiamide phosphate, urea phosphate and phosphates, pyrophosphates and polyphosphates of higher condensation products of melamine and/or melem and mixtures of these phosphates. The acids, salts, mixed acid salts, esters, partial esters and mixed esters of phosphates can also be used. Use may also be made of phosphine oxides, phosphine sulphides and phosphorinanes and of phosphonates, phosphites and phosphinates and of their acids, salts, mixed acid salts, esters, partial esters and mixed esters. The concentration of other flame-retarding components that can be used may vary within a wide range but will generally not be higher than the concentration of flame-retarding composition according to the invention. Preferably the amount will be between 0 and 35 wt. %, more in particular 1 and 20 wt. %. Preferably use is made of phosphates, phosphinates and phosphonates. Examples of such compounds are for example described in Kirk Othmer, Encyclopedia of Chemical Technology, Volume 10, pp. 396-419 (1980). Well-known examples are: the esters of trimethylol propane and methyl phosphonic acid, ethyl-methyl phosphinic acid and the aluminium salt of ethyl-methyl phosphinic acid. Many of the compounds mentioned here may also promote the formation of carbon. Other known compounds present in flame-retarding compositions such as polytetrafluoroethylene may also be present.
The polymer composition may also contain the other usual additives, such as heat and UV stabilisers, mould-release agents, plasticisers, softeners, lubricants, dispersing agents, colourants and/or pigments, in amounts generally used for these additives insofar as the properties are not adversely affected.
The polymer composition according to the invention can be prepared using the conventional techniques known per se, by for example mixing all or some of the components in dry condition in a tumble mixer, followed by melting in a melt mixer, for example a Brabender mixer or a single- or twin-screw extruder or a kneading machine. Preferably a twin-screw extruder is used.
The various components of the polymer composition of the invention may be dosed to the extruder""s throat together. They may also be dosed to the extruder in different places. Some of the components, for example colourants, stabilisers, the flame-retarding composition, compounds having a synergetic effect with the flame-retarding composition and/or other flame-retarding components may for example be added to the polymer in the form of a masterbatch.
The polymer composition according to the invention can be processed into semi-finished products or end products using techniques known to a person skilled in the art, for example injection-moulding.
The invention will be further elucidated with reference to the following examples:
Melamine (product of a gas-phase process from DSM) was dosed to a corotating twin-screw extruder (Werder and Pfleiderer, type ZSK 30/33) at a rate of 3 kg per hour. The cylinder temperature had been set to 330xc2x0 C. and the screw speed to 40 rpm. The residence time of the components dosed to the extruder was 115 seconds. The solid mixture leaving the extruder was white and had the following composition: 88 wt. % melamine, 6 wt. % melan, 2 wt. % melem and 4 wt. % higher condensation products of melamine and/or melem. The volatiles content is 1.6 wt. %. The composition of the flame-retarding composition was determined with the aid of high-pressure liquid chromatography (HPLC). The values obtained have a relative error of 5% or less.